1. Field of the Invention
The present invention relates generally to a channel estimation apparatus and method in a CDMA (Code Division Multiple Access) mobile communication system, and in particular, to an apparatus and method for performing channel estimation using power control bits in a CDMA mobile communication system.
2. Description of the Related Art
Generally, in order to perform communication, a mobile communication system establishes a channel and transmits/receives data over the channel. Transmission power of the channel is determined depending on a relative position of a mobile terminal to the base station. That is, a mobile terminal situated in a place far away from a base station must transmit data at higher power than a mobile station situated in a place relatively close to the base station, so that the base station can receive the transmitted data correctly. Controlling the transmission power from the base station to the mobile terminal is called “forward link power control”. Controlling transmission power from the mobile terminal to the base station is called “reverse link power control”. In the following description, the term “forward” as used herein refers to a direction from the base station to the mobile terminal, while the term “reverse” refers to a direction from the mobile terminal to the base station. In addition, the term “forward link” refers to a link established to transmit data from the base station to the mobile terminal, while the term “reverse link” refers to a link established to transmit data from the mobile terminal to the base station.
The base station detects a state of a channel received from the mobile terminal in order to perform the reverse link power control. That is, the base station detects a state of the channel over which a received signal has been transmitted, in order to perform coherent detection. Information on the channel state can be provided through a pilot channel. However, the existing mobile communication system performs only the forward link power control.
However, IMT-2000 system as a CDMA-2000 or WCDMA system, is designed to be able to use pilot signals even in the reverse link. Therefore, it is possible for the base station to perform coherent detection, thus contributing to smooth data transmission over the reverse link and an improvement in system capacity.
In addition, a channel estimator detects the channel state using the data received over the pilot channel. By doing so, the channel estimator estimates distortion of the signal. Further, the channel estimator can reduce distortion of information by applying the channel-estimated value to a received signal.
In a CDMA (Code Division Multiple Access) cellular system having limited cell capacity due to interference, the transmission power control is important to improving the overall cell capacity. In order to increase the cell capacity, the system may detect power control bits (PCBs) using a filter, and perform channel compensation based on the detected power control bits. For such a filter, various filters, especially, a WMSA (Weighted Multi-Slot Averaging) filter is used. In a mobile communication system receiving a pilot signal and a power control signal with power control bits among the bits in a predetermined period of a bit stream of the pilot signal, when the WMSA filter is used, time delay occurs in a channel compensation process using the power control bits, as illustrated in FIG. 6. Therefore, the channel estimator in the base station, using the WMSA filter, has low accuracy of closed-loop power control during analysis (discrimination) of power control bits on the reverse link.